Cross-linked polyvinyl butyral

Abstract

Polyvinyl butyral (PVB) resin lightly cross-linked through stable intermolecular linkages developed, for example, through use of a dialdehyde or trialdehyde, to selectively increase PVB molecular weight and the modulus of a plasticized sheet formed therefrom intended for use in laminated safety glass assemblies.

We claim: 
     
       1. A process for increasing the viscosity of polyvinyl butyral which comprises having a cross-linking agent present before or during acetalization of polyvinyl alcohol with butyraldehyde to lightly cross-link the acetalized product through adjacent polyvinyl alcohol chains, the extent of cross-linking being adequate to increase the viscosity of the polyvinyl butyral by about 2% to about 85% over its viscosity in the absence of said cross-linking agent, said polyvinyl butyral containing 65 to 95 weight % vinyl butyral units. 
     
     
       2. The process of claim 1 wherein the cross-linking agent is an aldehyde containing at least two aldehyde groups. 
     
     
       3. The process of claim 2 wherein the aldehyde is a trialdehyde or a dialdehyde containing an aliphatic or an aromatic group or a mixture of aliphatic and aromatic groups between carbonyl groups. 
     
     
       4. The process of claim 3 wherein the aldehyde is a trialdehyde. 
     
     
       5. The process of claim 3 wherein the aldehyde is a dialdehyde present at a concentration of about 0.0005 to about 0.20 parts per hundred parts of polyvinyl alcohol. 
     
     
       6. The process of claim 3 wherein the dialdehyde is selected from the group consisting of glutaraldehyde, 4,4'(ethylenedioxy) dibenzaldehyde and 2-hydroxyhexanedial. 
     
     
       7. The process of claim 6 wherein the dialdehyde is glutaraldehyde. 
     
     
       8. A method of forming polyvinyl butyral sheet which comprises: a. acetalizing polyvinyl alcohol with butyraldehyde in the presence of a cross-linking agent to produce polyvinyl butyral resin containing 65 to 95 weight % vinyl butyral units which is lightly cross-linked through stable intermolecular linkages, the extent of cross-linking being adequate to increase the viscosity of the polyvinyl butyral resin by about 2% to about 85% over its viscosity in the absence of said cross-linking agent;   b. mixing said resin with plasticizer and other optional additives to form an extrusion formulation; and   c. extruding said formulation in melt form through an extrusion opening without rupturing said cross-links to form said sheet.   
     
     
       9. The method of claim 8 wherein the cross-linking agent is an aldehyde containing at least two aldehyde groups. 
     
     
       10. The method of claim 9 wherein the cross-linking agent is a trialdehyde or a dialdehyde which contains an aliphatic or an aromatic group or a mixtures of aliphatic and aromatic groups between carbonyl groups. 
     
     
       11. The method of claim 10 wherein the aldehyde is a dialdehyde present at a concentration of about 0.0005 to about 0.20 parts per hundred parts of polyvinyl alcohol. 
     
     
       12. The method of claim 11 wherein the dialdehyde is selected from the group consisting of glutaraldehyde, 4,4'(ethylenedioxy) dibenzaldehyde and 2-hydroxyhexanedial. 
     
     
       13. The method of claim 12 wherein the dialdehyde is glutaraldehyde.